recognize as common header
(minor performance enhancement)
bug may result in long delays when using mod_deflate on connections
with keep-alive, as the result is sent without Content-Length or
(regression in lighttpd 1.4.51)
"high latency on 1.4.51 + proxy + deflate"
convert existing calls to manip request/response headers
convert existing calls to manip environment array (often header-related)